A catastrophic landslide induced by the 2018 Hokkaido Eastern Iburi earthquake occurred on a slope of distal tephra deposits, which is the largest historic landslides in Japan with an area of 13.4 km 2 . Such landslides do not occur on steep slopes because the tephra deposits themselves do not form slopes steeper than the angle of repose, and occur on gentle slopes shallower than 30°. Geochemical data for the pyroclastic fall deposits indicate sliding surfaces in halloysite-rich weathered pumice fall(loam)could facilitate the effective transfer of land slide mass on gentle slopes.